This invention relates to purification and recovery of amino acids from mixtures containing undesired impurities, for example, fermentation broths used in the microbial production of amino acids. As used in this application, the term amino acid means one of the naturally occurring amino carboxylic acids of which proteins are comprised.
Desired amino acids present at very low concentrations in complex mixtures often must be purified and recovered before they can be used. In particular, amino acids produced by a microorganism usually must be recovered from a fermentation broth containing nutrients, other amino acids, small peptides, other small organic compounds, and various larger components including cell debris, enzymes, and other proteins. Amino acids produced by chemical synthesis also must be recovered from a reaction medium containing raw materials and by-products.
Various methods of amino acid recovery have been disclosed. One specific method involves an ion exchange resin, often an anion exchange resin in a column, which binds the amino acid under certain conditions to separate it from the reaction mixture, and then releases the amino acid under other conditions to permit recovery of a crude solution of the amino acid. See, for example, Chem. Abstracts (1980) 93: 716, para. 93: 168613w; Yamada et al. (1981) Applied and Environmental Microbiology 42(5): 773-778; and Sakamoto et al., Chem. Abstracts (1979) 91: 1773363c.
The crude amino acid solution then may be further purified. For example, Chem. Abstracts (1980), cited above, discloses purifying the crude isolate obtained from the resin by treating the isolate with an organic acid to form a salt with the phenylalanine cation. The salt solution is adjusted to pH 5.48 to precipitate the pure phenylalanine.
Thunberg U.S. Pat. No. 3,904,585 discloses recovering amino acids, specifically alanine and glycine, by boiling to concentrate the solution and cooling to cause precipitation.